The present invention relates to a projector for projecting color images (projection display apparatus).
As a display having a large viewing surface, projectors for magnifying and projecting images on a screen are widely used. As the projectors known are a front type projector for projecting light rays on a reflection type screen and a rear-type projector for projecting light rays on a transmission type screen. As the rear-type projector, the technique disclosed in Japanese Unexamined Patent Application Publication No. 10-307332 has been exemplified.
In the rear-type projector, a light ray irradiated from a projecting device for projecting images is reflected by a plurality of mirrors so as to be projected on a screen. Of the plurality of mirrors, the reflecting mirror for reflecting the light ray to the screen is generally arranged to have an inclination of less than 45xc2x0 with respect to the screen, and by reducing the depth from the screen to this mirror, the rear-type projector is miniaturized.
As described above, when arranging the mirror for reflecting a light ray toward the screen, it is necessary to place the projecting device to slant relative to a plane perpendicular to the screen in order to compensate the rotation of an image to be projected on the screen. Accordingly, there is a difficulty in the positional adjustment of an optical system constituting a projector when slanting the projecting device to be placed corresponding to the inclination of the mirror.
The present invention has been made in order to solve the above-described problem in a conventional technique, and it is an object thereof to provide a technique capable of facilitating the positional adjustment of an optical system constituting a projector and also of miniaturizing the apparatus.
In order to solve at least part of the problem mentioned above, a projector according to the present invention comprises three electro-optical devices for forming images of three color components, a color-combining optical system for forming a color image by combining the images of three color components, a projection lens for projecting a color image formed by the color-combining optical system, a screen onto which the color image is projected, and first and second mirrors disposed on an optical path ranging from a plane of light incidence of the projection lens to a plane of light incidence of the screen for sequentially reflecting image light representing the color image emitted from the color-combining optical system. Furthermore, when three axes orthogonal to each other are referred to as an x-axis, a y-axis, and a z-axis, the screen is placed substantially in parallel with a yz-plane, and the color-combining optical system, having two kinds of dichroic surfaces arranged substantially in an X-shape, is placed so that a line of intersection between the two kinds of dichroic surfaces is to be substantially parallel to the z-axis. Also, each of the electro-optical devices, having a substantially rectangular image-forming region, is placed so as to face a corresponding plane of incidence out of three planes of incidence parallel to the line of intersection of the color-combining optical system so that the direction of the longer side of the image-forming region agrees with the direction of the line of intersection. Moreover, a reflection surface of the first mirror is arranged substantially perpendicularly to the yz-plane and also with an inclination of approximate 45xc2x0 relative to an xy-plane, and at least the electro-optical devices, the color combining optical system, and the projection lens are arranged along the xy-plane so that an image light emitted from the color-combining optical system enters the first mirror with its optical-axis parallel to the xy-plane and inclined xcex1xc2x0 with respect to the y-axis. Also, the second mirror is placed substantially perpendicularly to an xz-plane with an inclination of smaller by xcex1/2xc2x0 than 45xc2x0 approximately with respect to the yz-plane so that an image light reflected from the first mirror is reflected by the second mirror again so as to enter the screen with the optical axis being incident on the substantial center of the screen and substantially perpendicular to the screen.
In the projector according to the present invention, the second mirror for reflecting image light from the first mirror to be incident on the screen can be arranged substantially perpendicularly to the xz-plane with an inclination of smaller by xcex1/2xc2x0 than 45xc2x0 approximately with respect to the yz-plane, so that the depth from the screen to the second mirror can be reduced. Thereby, the apparatus can be miniaturized. At least the electro-optical device, color combining system, and projection lens are arranged along a plane substantially perpendicular to the screen (horizontal plane, for example), so that the arrangement or positional adjustment involved in the arrangement of these optical components can be facilitated. Therefore, in the projector according to the present invention, the arrangement of the optical system constituting the projector can be facilitated, and the apparatus can be miniaturized as well.
In the projector described above, the first mirror may be preferably integrally arranged with the projection lens.
By such a structure, the arrangement space for the first mirror can be reduced, so that the apparatus can be miniaturized. In addition the meaning of xe2x80x9cbeing integrally arrangedxe2x80x9d includes not only being integrally arranged combined with the vicinity of the incidence plane or the emission plane of the projection lens but also being arranged within the projection lens.
Wherein the first mirror may be preferably formed of a total reflection prism.
By such a structure, the reflectance of the first mirror can be increased and bright projection images can be readily achieved.